TWI626522B - Power point tracking method and apparatus thereof - Google Patents

Abstract

A power point tracking method and device thereof, including a transducer coupled to a controller, wherein the transducer can use an internal inductor of the transducer to perform power conversion operations according to a duty cycle signal of the controller, to Convert the input voltage supplied by the hunting device to the output voltage to the load.

Description

Power point tracking method and device

The present disclosure relates to a power point tracking method and device.

Generally speaking, renewable energy currently accounts for only a small part of the world ’s electricity. However, due to the limited petrochemical fuel and the negative impact on the environment, the renewable energy technology needs to develop upwards. It is a substitute for petrochemical fuel, and can further collect energy for reuse in the environment, especially with thermoelectric materials (TEM) and energy harvesting (EH) as popular research topics.

There are many energy sources with maximum power point (MPP) characteristics. For example, FIG. 1 shows a characteristic curve of output current and output voltage of a thermoelectric (TE) energy source (thermoelectric material), and a characteristic curve of output voltage and output power. In the graph at the top of FIG. 1, the horizontal axis represents the output voltage V _{TE of the} thermal voltage source, and the vertical axis represents the output current I _{TE of the} thermal voltage source. In the graph in the lower part of FIG. 1, the horizontal axis represents the output voltage V _{TE of the} thermal voltage source, and the vertical axis represents the output power P _{TE of the} thermal voltage source. As can be seen from FIG. 1, when the output current I _{TE of} the thermal voltage source is larger, the output voltage V _{TE is} smaller. When the output voltage V _{TE of the} thermal voltage source is set at the operating voltage V _OP shown in FIG. 1, its output power P _TE can reach the maximum power value P _MAX (ie, the maximum power point).

For another example, FIG. 2 illustrates a characteristic curve of output current and output voltage of a photovoltaic cell (PV), and a characteristic curve of output voltage and output power. In the upper graph of FIG. 2, the horizontal axis represents the output voltage V _{PV of the} photovoltaic cell, and the vertical axis represents the output current I _{PV of the} photovoltaic cell. In the graph in the lower part of FIG. 2, the horizontal axis represents the output voltage V _{PV of the} photovoltaic cell, and the vertical axis represents the output power P _{PV of the} photovoltaic cell. It can be seen from FIG. 2 that when the output current I _{PV of} the photovoltaic cell is larger, the output voltage V _{PV is} smaller. When the output voltage V _{PV of the} photovoltaic cell is set at the operating voltage V _OP shown in FIG. 2, its output power P _PV can reach the maximum power value P _MAX (ie, the maximum power point).

Therefore, in the process of how to use energy with Maximum Power Point (MPP) characteristics, it is necessary to perform power point tracking on the output of this energy to improve the efficiency of power generation as an important issue.

The present disclosure provides a power point tracking method and device that can track the output power point of an energy source.

According to an embodiment of the disclosure, the power point tracking method includes: a controller obtains a first operating point and a first characteristic curve according to an open circuit voltage or an input voltage of an energy hunting device, the controller according to the first operating point, A transducer characteristic, an output voltage and a desired operating point are used to calculate a first duty cycle signal. The transducer operates after receiving the first duty cycle signal. The controller is based on the input voltage and the output voltage And the first duty cycle signal calculates a second operating point and obtains a second characteristic curve; and the controller uses the second characteristic curve, the transducer characteristic, the output voltage and the desired operating point to A second duty cycle signal is calculated and sent to the transducer for tracking control.

According to another embodiment of the present disclosure, the power point tracking device includes a turn The energy converter is coupled to a controller; wherein the energy converter can use the internal inductor of the energy converter to perform power conversion operation according to a duty cycle signal of the controller, so as to convert the input voltage supplied by the energy hunter to the output Voltage to the load.

In order to make the above-mentioned features and advantages of the present disclosure more comprehensible, the embodiments are specifically described below and described in detail in conjunction with the accompanying drawings.

10‧‧‧ energy hunting device

20‧‧‧load

310‧‧‧Transducer

320‧‧‧Controller

S410 ~ 450, S610 ~ S680 ‧‧‧ steps

510‧‧‧Analog digital transducer

520‧‧‧ processor

530‧‧‧ duty cycle generator

540‧‧‧model generator

FIG. 1 shows the characteristic curves of output current and output voltage of thermoelectric (TE) energy (thermoelectric material), and the characteristic curves of output voltage and output power.

FIG. 2 shows the characteristic curve of output current and output voltage of photovoltaic cell (PV), and the characteristic curve of output voltage and output power.

FIG. 3 is a schematic block diagram of a power point tracking device according to an embodiment of the invention.

FIG. 4 is a schematic flowchart illustrating a power point tracking method according to an embodiment of the invention.

FIG. 5 illustrates an example of a circuit implementation of the controller.

FIG. 6 is a schematic flowchart illustrating a power point tracking method according to another embodiment of the invention.

FIG. 7 is a schematic diagram of the current characteristic curve provided for explaining the operation of the inductor.

FIG. 8 is a schematic diagram illustrating the operation of the transducer shown in FIG. 3 in discontinuous current mode (DCM) and continuous current mode (CCM).

9 is a schematic circuit diagram illustrating a buck transducer according to an embodiment of the present invention, and a waveform timing diagram of the buck transducer operating in a discontinuous current mode (DCM).

FIG. 10 is a schematic circuit diagram illustrating a boost converter according to another embodiment of the present invention, and a waveform timing diagram of the boost converter operating in a discontinuous current mode (DCM).

The term "coupled" used in the entire specification of this case (including the scope of patent application) may refer to any direct or indirect connection means. For example, if it is described that the first device is coupled to the second device, it should be interpreted that the first device can be directly connected to the second device, or the first device can be connected through other devices or some connection Indirectly connected to the second device. In addition, wherever possible, elements / components / steps using the same reference numbers in the drawings and embodiments represent the same or similar parts. Elements / components / steps that use the same reference numbers or use the same terminology in different embodiments may refer to related descriptions with each other.

FIG. 3 is a schematic block diagram of a power point tracking device according to an embodiment of the invention. The power point tracking device shown in FIG. 3 includes a transducer 310 and a controller 320. The controller 320 may be a digital controller, which may include one or more analog digital transducers. The transducer 310 may be a synchronous DC-DC converter, an asynchronous DC-DC converter, or other Power transducer. For example, the transducer 310 may be a boost (Boost) transducer, a buck (Buck) transducer, a buck-boost (Buck-Boost) transducer, a flyback (Flyback) transducer, a SEPIC transducer Transducer, Cúk transducer, or other transducer that uses an inductor L for power conversion operation, the transducer 310 can use the internal of the transducer 310 according to the duty cycle signal of the controller 320 The inductor performs a power conversion operation to convert the input voltage supplied by the hunting device 10 to the output voltage to the load 20. For example, the transducer 310 may use the output voltage to charge the load 20, where the load may be a battery, but is not limited thereto.

The energy hunting device 10 has a maximum power point (Maximum Power Point, MPP) characteristic. For example, the energy harvester 10 is a fuel cell (Fuel Cell), a thermoelectric harvester (Thermoelectric Harvester), a light harvester (Photovoltaic Harvester), a piezoelectric harvester (Piezoelectric Harvester) or limited energy and DC characteristic device. The controller 320 needs to monitor the output current of the hunter 10 through the input current of the transducer 310. Therefore, the controller 320 can track the maximum power point of the hunter 10 according to the output current information of the hunter 10, that is, The controller 320 can control the charging operation of the load 20 according to the output current information of the transducer 310.

FIG. 4 is a schematic flowchart illustrating a power point tracking method according to an embodiment of the invention. 3 and 4, in step S410, a controller obtains a first operating point and a first characteristic curve according to the open circuit voltage or input voltage of an energy hunting device; in step S420, the controller according to the The first operating point, a transducer characteristic, an output voltage, and a desired operating point are used to calculate a first duty cycle signal; the transducer operates after receiving the first duty cycle signal (step S430), the control The controller calculates a second operating point according to the input voltage, the output voltage and the first duty cycle signal, and obtains a second characteristic curve (step S440); and the controller according to the second characteristic curve and the energy conversion The characteristics of the transducer, the output voltage and the desired operating point are used to calculate a second duty cycle signal, which is transmitted to the transducer for tracking control (step S450). In order to convert the input voltage E _IN supplied by the hunting device 10 into the output voltage E _OUT to the load 20. The load 20 may be a resistive load, a capacitive load, or an inductive load. For example, the transducer 310 may use the output voltage E _OUT to charge the load.

In the no-load condition, the controller 320 sets the operating point to meet the output load size requirement, so that the total energy is balanced. Therefore, during steady-state operation, the operating point multiplied by the transducer efficiency will be the same as the load. When there is a load, the controller will simultaneously evaluate the maximum acceptable energy of the load and the load size as the calculation of the operating point. When the maximum acceptable energy of the battery plus the load size is greater than the maximum energy of the energy hunter in the controller, The controller will control the energy transfer at the set optimal operating point. When the result is less than the maximum energy of the energy hunter, in steady state operation, the operating point will be multiplied by the energy efficiency of the energy converter, and it will be the maximum acceptable energy and the sum of the load. the same.

FIG. 5 illustrates a circuit implementation example of the controller 320. The controller 320 further includes an analog digital transducer 510, a processor 520, a duty cycle generator 530, and a model generator 540, and the model generator 540 provides a characteristic curve. To the processor. The controller 320 can adopt the Pulse Width Modulator (PWM) method, Pulse Skip Modulator (PSM) method, Pulse Frequency Modulator (PFM) method, Σ- △ Modulation (Sigma-Delta Modulator, SDM) mode or burst modulation (Burst Modulator) mode. The controller 320 and the transducer 310 can be operated in a discontinuous current mode (Discontinue Current Mode, DCM) or a continuous current mode (Continue Current Mode, CCM), where the processor 520 is a special application integrated circuit (ASIC) ), A microprocessor (MCU), a processor (Processor), a controller (Controller), the model generator can be a hunter, or a limited energy or AC type rectified hunter or limited energy , But not limited to this.

The duty cycle generator 530 is a digital pulse width modulation generator, or a digital-to-analog converter (DAC) and a sawtooth generator (Sawtooth Generator) through a comparison Comparator to generate the duty cycle signal.

FIG. 6 is another example of the power tracking method. The input power is calculated based on the input voltage and input current, and the operating point is confirmed (step S610); whether or not the hunter modeling is performed (step S620); Establish or modify the characteristic curve of the hunter (step S630); the controller calculates the duty cycle signal based on the operating point, characteristic curve, transducer characteristics, output voltage and desired operating point (step S640); delay for a period of time, based on Calculate the input power for the voltage and input current, and confirm the operating point (step S650); determine whether it is the same as the desired operating point (step S660); if it is the same, continue with step S650, if not, return to step S630. If the hunting device cannot be modeled, the first operating point is recorded (step S670), and the controller adjusts the duty cycle signal according to the first operating point (step S680), and returns to step S610 again.

FIG. 7 is a schematic diagram illustrating the current characteristic curve of the inductor L in the transducer 310 shown in FIG. 4. In the right graph of FIG. 7, the horizontal axis represents time T, and the vertical axis represents the current value I _{L of the} inductor _L. According to equation (1), the controller 320 can calculate the current value I _L dI _L = ( 1 / L ) ʃ of the inductor L from the voltage V _L across the inductor L, the inductance value L of the inductor L, and the time T V _L dt formula (1)

FIG. 8 is a schematic diagram illustrating the operation of the internal inductor L of the transducer 310 shown in FIG. 4 in a discontinuous current mode (DCM) and a continuous current mode (CCM), respectively. The upper part of FIG. 8 shows the waveform timing diagram of the duty cycle signal, in which the horizontal axis represents time and the vertical axis represents the amplitude of the duty cycle signal. The middle part of FIG. 7 shows a schematic diagram of the current waveform of the inductor L operating in the discontinuous current mode (DCM), where the horizontal axis represents time and the vertical axis represents the current I _{L of the} inductor _L. In the discontinuous current mode (DCM), the controller 320 may start with both ends of the inductor L during the cross voltage V _L and the energy storage inductor L T _SE, to calculate the period T _SE in the storage inductor L Current change △ _ISE . Next, calculate the energy release period T _RE . The information of the average current I _AVG , output current I _O and power of the inductor L can be calculated from △ _ISE , T _SE , T _RE and the period T _{P of the} duty cycle signal. Information about the average current I _AVG , output current I _O and / or power of the inductor L can be used as the duty cycle signal. With the duty cycle signal, the controller 320 can track the power point of the input energy E _IN .

The lower part of FIG. 8 shows a schematic diagram of the current waveform of the inductor L operating in the continuous current mode (CCM), where the horizontal axis represents time and the vertical axis represents the current I _{L of the} inductor _L. In the continuous current mode (CCM), the controller 320 may start with both ends of the inductor L during the cross voltage V _L and the energy storage inductor L T _SE, L to calculate the current during the energy storage inductor T _SE Change △ _ISE . Next, and then calculated by the T _RE can release the energy during the release period T _RE inductor L current variation △ _IRE can be obtained in the next cycle the inductor L T _P starting current I _0. In the next period T _P, the inductor L can calculate the average power or the current I _AVG △ _ISE, △ _IRE and I _0. Information about the average current I _AVG or power of the inductor L can be used as the duty cycle signal. With the duty cycle signal, the controller 320 can track the power point of the input energy E _IN .

3 and 9, the power switch M1 is controlled by the duty cycle signal. According to the operation of the duty cycle signal, the power switch M1 can divide the power conversion operation into an inductive energy storage (Store Energy) operation and an inductive energy release (Release Energy) operation. During the energy storage period, the power switch M1 is turned on, so the current of the input energy E _IN can be stored in the inductor L and the capacitor C1 through the power switch M1. During the energy release period, the power switch M1 is turned off. At this time, the inductor L can provide current from the diode D1 to the capacitor C1 and the load 20.

The lower part of FIG. 9 shows the waveform timing diagram of the duty cycle signal, in which the horizontal axis represents time, and the vertical axis represents the amplitude of the duty cycle signal. 9 shows a schematic diagram of the current waveform of the inductor L operating in the discontinuous current mode (DCM), where the horizontal axis represents time and the vertical axis represents the current I _{L of the} inductor _L. When the inductor L is operating during the energy storage period, the controller 320 may calculate equation (2) to calculate the voltage difference V _{L of the} inductor _L. In equation (2), V _IN is the voltage value of the input voltage E _IN , V _M1 is the turn-on voltage drop of the power switch M1, and V _OUT is the voltage value of the output voltage E _OUT .

V _L = V _IN -V _M1 -V _OUT formula (2)

After obtaining the voltage difference V _L of the inductor L, the controller 320 may calculate the formula (1), and obtain the current value I _{L of the} inductor _L , as shown in the formula (3). In equation (3), L is the inductance value of the inductor L, and T1 and T0 are the upper and lower bounds of time, respectively.

After obtaining the current value of the d _IL, the controller 320 may calculate Equation (4), to obtain the current value of the inductor L during storage T _SE I _SE. In equation (4), I0 is the current value of the inductor L at time T0. Since the transducer 310 operates in the discontinuous current mode (DCM), the initial current value I ₀ of the inductor L at time T0 is 0. The energy storage period T _SE is the duty cycle of the duty cycle signal (that is, the power switch M1 is the on-time).

Therefore, in other embodiments, the controller 320 may further calculate the formula (5) to obtain the input power Pop. In equation (5), V _{op and} I _op are the input voltage and current, respectively, and the duty cycle signal is obtained.

The following will use a boosted transducer as an example of implementation of the transducer 310. For example, FIG. 9 is a schematic circuit diagram illustrating a step-up transducer (transducer 310) according to another embodiment of the present invention, and the step-up transducer (transducer 310) operates in a discontinuous current mode (DCM) ) Waveform timing diagram.

3 and 10, the power switch M1 is controlled by the duty cycle signal. According to the duty cycle operation of the duty cycle signal, the power switch M1 can divide the power conversion operation into an inductive energy storage operation and an inductive energy release operation. During the energy storage period, the power switch M1 is turned on, so the current of the input energy E _IN can be stored in the inductor L. During the energy release period, the power switch M1 is turned off. At this time, the inductor L can provide current from the diode D1 to the capacitor C1 and the load 20.

The lower part of FIG. 10 shows the waveform timing diagram of the duty cycle signal, in which the horizontal axis represents time and the vertical axis represents the amplitude of the duty cycle signal. 10 shows a schematic diagram of the current waveform of the inductor L operating in the discontinuous current mode (DCM), where the horizontal axis represents time and the vertical axis represents the current I _{L of the} inductor _L. When the inductor L operates during the energy storage period, the controller 320 may calculate equation (6) to calculate the voltage difference V _{L of the} inductor _L. In equation (6), VIN is the voltage value of the input energy E _IN , and V _M1 is the turn-on voltage drop of the power switch M1.

V _L = V _IN -V _M1 formula (6)

After obtaining the voltage difference V _L of the inductor L during the energy storage period T _SE , the controller 320 may calculate the formula (1), and obtain the current value I _{L of the} inductor _L , as shown in the formula (7). In equation (7), L is the inductance value of the inductor L, and T1 and T0 are the upper and lower bounds of time (storage period), respectively.

After obtaining the current value of the d _IL, the controller 320 may calculate the equation (8), to obtain the current value of the inductor L during the period T _SE of the storage I _SE. In equation (8), I ₀ is the current value of the inductor L at time T0. Since the transducer 410 operates in the discontinuous current mode (DCM), the initial current value I ₀ of the inductor L at time T0 is 0. The energy storage period T _SE is the duty cycle of the duty cycle signal (that is, the power switch M1 is the on-time).

When the inductor L operates during the energy release period T _RE , the controller 320 may calculate equation (9) to calculate the voltage difference V _{L of the} inductor L during the energy release period T _RE . In equation (9), V _OUT is the voltage of the output energy V _OUT , V _D1 is the forward voltage drop of the diode D1, and V _IN is the voltage value of the input energy E _IN . In some embodiments, the forward voltage drop V _{D1 of the diode D1} may be a fixed value. Or an approximate value for obtaining the forward voltage drop V _D1 of the diode D1 can be obtained through a simple calculation formula.

V _L = V _OUT + V _D1 -V _IN formula (9)

After obtaining the voltage difference V _L of the inductor L during the energy release period T _RE , the controller 420 can calculate the formula (1), and obtain the current value dI _L ′ of the inductor L during the energy release period T _RE and the energy release period T _RE , As shown in equation (10). In equation (10), T1 and T2 are the upper and lower bounds of time (the energy release period T _RE ), respectively.

So far, in some other embodiments, the controller 320 may further obtain the input power Pop according to the calculation formula (5), and then obtain the duty cycle signal.

In summary, the power point tracking device and method of the disclosed embodiment can track the output power point of the hunting device 10 by the duty cycle signal. Then the power of the hunting device 10 can be tracked.

Although this disclosure has been disclosed as above with examples, it is not intended to limit this disclosure. Any person with ordinary knowledge in the technical field can make some changes and retouching without departing from the spirit and scope of this disclosure. The scope of protection disclosed in this disclosure shall be subject to the scope defined in the appended patent application.

Claims (22)

A power point tracking method includes: a controller acquiring a current-voltage relationship curve of an energy hunter, the energy hunter is coupled to the controller and a transducer, and the transducer is received from the energy hunter A current and an input voltage, and output an output voltage, the current-voltage relationship curve is the relationship between the current and the input voltage of the hunter; the controller inputs the current, the input voltage, the following equation A duty cycle is calculated for the conduction voltage drop of one of the power switches of the transducer, the output voltage and the inductance value of an inductor of the transducer

, Where I _{SE is} the current, V _{IN is} the input voltage, V _M1 is the conduction voltage drop of the power switch of the transducer, V _{OUT is} the output voltage, T _{SE is} the duty cycle, and L is the transition The inductance value of the inductor of the energy converter; the energy converter operates for a period of time after receiving the duty cycle; the controller inputs the duty cycle and the conduction voltage drop of the power switch of the energy converter according to the above equation , The output voltage and the inductance value of the inductor of the transducer, the relationship between the current and the input voltage is obtained to update the current-voltage relationship curve; and the controller relies on the updated current-voltage relationship Curve, tracking the power point of the energy hunting device. The power point tracking method according to claim 1, wherein the transducer is a direct current transducer. The power point tracking method according to claim 2, wherein the transducer includes a synchronous DC-DC converter and an asynchronous DC-DC converter. The power point tracking method according to claim 2, wherein the transducer includes a boost transducer, a buck transducer, a buck-boost transducer, a flyback transducer, and a SEPIC Transducer or a Cúk transducer. The power point tracking method according to claim 1, wherein the controller further includes an analog digital transducer, a processor, a duty cycle generator, and a model generator. The power point tracking method according to claim 5, wherein the controller is a digital controller. The power point tracking method according to claim 6, wherein the digital controller includes one or more analog digital transducers. The power point tracking method as described in claim 5, wherein the processor is a special application integrated circuit (ASIC), a microprocessor (MCU), a processor (Processor), and a controller (Controller). The power point tracking method according to claim 5, wherein the model generator provides the current-voltage relationship curve to the processor. The power point tracking method according to claim 9, wherein the model generator is a finite energy source and an AC type rectified energy hunter limited energy source. The power point tracking method according to claim 1, wherein the controller and the transducer are operated in a discontinuous current mode or a continuous current mode. A power point tracking device includes a transducer; and a controller coupled to the transducer and an energy hunter, the controller obtains a current-voltage relationship curve of the energy hunter, the energy hunter is coupled Connected to the controller and a transducer, the transducer receives a current and an input voltage from the hunter, and outputs an output voltage, and the current-voltage relationship curve is the current and the hunter The relationship between the input voltage; the controller inputs the current, the input voltage, the turn-on voltage drop of one of the power switches of the transducer, the output voltage and the inductance of one of the inductors of the transducer in the following equation Value, calculate a duty cycle,

, Where I _{SE is} the current, V _{IN is} the input voltage, V _M1 is the conduction voltage drop of the power switch of the transducer, V _{OUT is} the output voltage, T _{SE is} the duty cycle, and L is the transition The inductance value of the inductor of the energy converter; the energy converter operates for a period of time after receiving the duty cycle; the controller inputs the duty cycle and the conduction voltage drop of the power switch of the energy converter according to the above equation , The output voltage and the inductance value of the inductor of the transducer to obtain the relationship between the current and the input voltage to update the current-voltage relationship curve; the controller according to the updated current-voltage relationship curve , To track the power point of the energy hunting device. The power point tracking device according to claim 12, wherein the controller further includes an analog digital transducer, a processor, a duty cycle generator, and a model generator. The power point tracking device according to claim 12, wherein the controller is a digital controller. The power point tracking device according to claim 14, wherein the digital controller includes one or more analog digital transducers. The power point tracking device according to claim 12, wherein the transducer is a DC-DC converter. The power point tracking device according to claim 16, wherein the transducer includes a synchronous DC-DC converter and an asynchronous DC-DC converter. The power point tracking device according to claim 17, wherein the transducer includes a boost transducer, a buck transducer, a buck-boost transducer, a flyback transducer, and a SEPIC transducer Transducer or a Cúk transducer. The power point tracking device according to claim 13, wherein the processor is an application specific integrated circuit (ASIC), a microprocessor (MCU), a processor, and a controller. The power point tracking device according to claim 13, wherein the duty cycle generator is a digital pulse width modulation generator for generating the duty cycle. The power point tracking device according to claim 13, wherein the duty cycle generator is a digital-to-analog converter (DAC) and a sawtooth generator (Sawtooth Generator) through a comparator ( Comparator) to generate this duty cycle. The power point tracking device according to claim 12, wherein the energy harvester is a fuel cell (Fuel Cell), a thermoelectric harvester (Thermoelectric Harvester), a light harvester (Photovoltaic Harvester), piezoelectric hunting Energy harvester (Piezoelectric Harvester) or a device with limited energy and DC characteristics.